A preferred field of application for the invention is that of inspecting fastener holes in a turbomachine disk, e.g. in an airplane engine.
Using eddy currents for non-destructive inspection consists in moving an electromagnetic sensor (a coil carrying a high frequency current) in the vicinity of a metal part for inspection, and in identifying defects (in particular non-uniformities or cavities) by detecting variations in the impedance of the sensor on passing in the vicinity of such a defect.
Such a sensor needs to be calibrated regularly with the help of a calibration part having known characteristics (e.g. including no detectable defect) that is pierced by a hole similar to the hole(s) for inspection. A hole is said to be “similar” when it comprises a borehole or a cavity having the same shape and dimensions. If it is a cavity, it need not necessarily be closed, such as the cavity of a blade root, for example.
More precisely, for the above-mentioned rotor disks, it is necessary to inspect the fastener holes in the manner mentioned above not only at the end of fabrication, but also, and mainly, during inspection for maintenance purposes. It is known to make use of an eddy-current probe carried by a drive system mounted on a support made of insulating material. The probe is installed at the end of a rod that is driven both in rotation about and in translation along its own axis. For example, the probe may have a rounded end (spherical or ellipsoidal in shape) that is split so as to present a certain amount of resilience and that includes an above-mentioned sensor. The resilience guarantees contact between the outside surface of the probe and the inside surface of the hole.
The probe is installed at the end of a rod that is driven both in rotation about and in translation along its own axis. The drive system is mounted on a support that is positioned over the orifice of a hole for inspection, and the probe is engaged in the hole in order to explore the entire surface thereof.
For calibration purposes, an operator needs to move the entire support carrying the probe and its drive means to a special stand carrying the calibration part, in order to explore completely the hole in the calibration part.
In practice, calibration is repeated once every ten holes, thereby leading to a significant loss of time, and in addition the process is not entirely satisfactory since it implies manual intervention and a change in frame of reference, thereby degrading the accuracy and the reliability of the calibration.
The invention enables those drawbacks to be overcome.